diff --git a/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala b/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala
index e5e1e72cd912bc5435b9126a9e0692e290df9b35..578d8062630069956ece99e158b952e86ff6999f 100644
--- a/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala
+++ b/core/src/main/scala/org/apache/spark/network/ConnectionManager.scala
@@ -851,8 +851,8 @@ private[spark] class ConnectionManager(
         messageStatuses.synchronized {
           messageStatuses.remove(message.id).foreach ( s => {
             promise.failure(
-              new IOException(s"sendMessageReliably failed because ack " +
-                "was not received within ${ackTimeout} sec"))
+              new IOException("sendMessageReliably failed because ack " +
+                s"was not received within $ackTimeout sec"))
           })
         }
       }